Spotting the Needle in a Haystack

The Importance of X-ray Systems in Quality Control for Food and Pharmaceutical Lines

There are no legal requirements to use x-ray inspection. However guidelines such as Hazard Analysis Critical Control Points (HACCP), the Global Food Safety Initiative, and the FDA’s Good Manufacturing Practice, as well as ad hoc standards set by individual retailers put the responsibility on product manufacturers to establish reliable product inspection programmes.

X-ray technology is one product inspection technology that is heavily used by the food and pharmaceutical industries. However, users in many other industries including medical diagnostics, security and construction for applications such as structural, mining and engineering rely on and trust x-ray technology for a host of needs. In the medical world, for example, x-rays are used to ‘see’ what is happening inside the body; for security applications they can ‘look’ inside baggage or parcels to check that contents are safe. For each industry, x-ray systems are specialised, efficient and advanced.

One of the main purposes of x-ray technology in the food and pharmaceutical industries is to inspect products or packages for the presence of foreign bodies or contaminants such as glass, ceramics, metal, stone or bone. But how exactly do x-ray systems find foreign bodies? What are typical contaminants? What are the issues manufacturers face when using x-ray systems to detect foreign bodies in products and packaging? Why does x-ray have such a growing role in product inspection? Taking a holistic view of x-ray technology for product inspection in the food and pharmaceutical industries will help to find the answers.

A closer look at x-ray

X-rays are one of several naturally-occurring sources of radiation, and are an invisible form of electromagnetic radiation, like light or radio waves. All types of electromagnetic radiation are part of a single continuum known as the electromagnetic spectrum. The spectrum runs from long-wave radio at one end to gamma rays at the other.

The wavelength of x-rays enables them to pass through materials that are opaque to visible light. The transparency of a material to x-rays is broadly related to its density: the denser the material, the fewer x-rays pass through. Dense materials, including foreign bodies like glass, bone and metal, show up on scans because they reflectmore x-rays than the surrounding material.

To the contrary of myths that say x-rays are dangerous, x-ray inspection systems are safe by design. They generate x-rays only when the unit is switched on. During that period, the risk of being exposed to radiation can be controlled by keeping an appropriate distance from the x-ray generator and through shielding around the x-ray beam. Typically, the entire assembly is encased in a stainless steel x-ray cabinet with a highly visible lamp stack that signals if the system is operating and therefore emitting radiation.

X-rays used in food and pharmaceutical inspection lines should not be associated with radioactive materials such as uranium, which are physical sources of radiation that continuously emit radiation. X-rays used in food inspection are different. Like light from a bulb, they can be turned on and off. Switch off the electricity supply to the x-ray system, and the flow of x-rays ceases instantaneously.

Using x-ray machines for the inspection of food and pharmaceutical products has become more and more popular due to increasingly stringent food safety and quality standards and the technology’s successful eradication offoreign bodies. Faster line speeds and rising consumer demands for product quality make extremely reliable methods of product inspection necessary. Scientific evidence has shown that x-rays do not harm our food in any way. The World Health Organisation (WHO) even confirmed that food radiation levels up to 10,000 Sv (Sievert) do not affect food safety or nutritional value. This means that food could be subject to radiation doses around ten million times stronger than those used in x-ray inspection without any harmful effects.

X-ray systems for product inspection

For food and pharmaceutical product inspection, an x-ray system uses an x-ray generator to project a beam of low energy x-rays onto a sensor or detector. X-ray inspection involves passing a product or pack through the x-ray beam before it reaches the detector. The amount of x-ray energy absorbed during the beam’s passage through a product is affected by the product thickness, density and its atomic mass number. When the product passes through the x-ray beam, only the residual energy reaches the detector as the x-ray beam passes through the product or pack being inspected, before finally reaching the detector. The measurement of differences in absorption between the product and a contaminant is the basis of foreign body detection in x-ray inspection. Hidden contaminants show up with x-ray inspection because they absorb more x-rays than the surrounding food.

The three key components of an x-ray inspection system are an x-ray generator, a detector and a computer. The x-ray beam is generated by an x-ray tube encased in the x-ray generator. It leaves via an exit window and travels in a straight line through a collimator device that narrows the stream of x-rays to a smaller fan beam. The x-ray beam then passes through the product or pack being inspected, before finally reaching the detector.

Tailored x-rays

According to the needs of manufacturers there are two types of x-ray tube: a glass tube to produce a low contrast image and a beryllium tube with softer x-ray energy for higher contrast images. A glass tube is the most common type because its penetration abilities suit a wide variety of applications. When the product to be inspected is of low density and small in depth – which is typically less than 30 millimetres – a beryllium tube can be used instead of glass. This lower-energy tube creates softer x-rays, which give better contrast and better detection levels on medium-density contaminants like glass, mineral stone or bone.

The geometry of the x-ray beam is another adaptation that can be made. Most x-ray systems use a vertical x-ray beam from the generator to scan the product as it passes through the x-ray system. Horizontal systems use a side-mounted x-ray generator to scan products passing on the conveyor belt, and are generally used for vertically-oriented products or packs that are taller than they are wide.

Also, multiple x-ray beams can be applied rather than a single beam to optimise the probability of detection. Two x-ray beams from a single generator, also known as a split beam, increase the probability of detection of foreign bodies as two images are created from different angles simultaneously. This is particularly useful for packaging such as metal cans where it is difficult to detect a contaminant close to the can wall due to the angle of the image. More specifically, the arrangement means that a larger area of the base or crown is inspected, which makes it easier to spot contaminants located on the side wall as they appear nearer the centre on one of the images.

Dual x-ray beams from separate generators similarly increase detection by providing images from two opposing angles. Products packaged in glass bottles or jars can be amongst the most challenging to inspect since the base, sidewalls and neck can cause ‘blind spots’ when inspected with a single x-ray beam. In this instance multiple x-ray beams are used. For example, one vertical and three horizontal x-ray beams will scan the product simultaneously to produce a series of images from a range of angles. The angled beams reduce blind spots and optimise detection.

Importance of x-ray in the food and pharmaceutical industries

Since the early 1990s, the food and pharmaceutical industries have relied on x-ray technology to detect potentially harmful foreign bodies so they can protect consumers and maintain their brand reputations. The reason that x-ray inspection is so useful in food and pharmaceutical manufacturing is because hidden foreign bodies are often easy to identify.

X-ray inspection is able to detect foreign bodies such as glass, metal, stone, bone, high- density plastics, and rubber compounds. The technology is also extremely adept at detecting ferrous, non-ferrous, and stainless-steel metals, even in products that are packaged in cans, metallised film or foil. Also, x-ray systems can be used to identify foreign bodies in a range of applications from raw products in bulk flow to packaged ready meals, products pumped through a pipeline to products in glass jars, bottles or metal cans. Even products in blister packs or sachets can be inspected.

Another reason for the growing importance of x-ray technology in the food and pharmaceutical industries is its diversified application possibilities. Manufacturers do not just use x-ray inspection to detect contaminants. X-ray systems can also perform a wide range of in-line quality checks such as measuring the mass of a product, counting components, identifying missing or broken products, monitoring fill levels, inspecting the integrity of a product seal or closure, as well as checking for damaged products and packaging. These tasks can be performed simultaneously, so the product only passes through the x-ray beam once.

Finding them all

A company-wide product inspection programme that ensures product safety and quality helps food manufacturers comply with national and international regulations, local legislation, and standards set by retailers.

X-ray inspection is increasingly being used in the food and pharmaceutical industries. With each passing year, more well-known brands are using x-ray inspection systems to detect foreign bodies and to reject contaminated product from the production line. X-ray inspection systems give manufacturers the tools they need to maintain quality control and product integrity at every stage of production. The product that successfully passes x-ray inspection contains no shocks, surprises, or disappointments. The manufacturer knows that it fulfils its brand promise.